This invention relates to internal combustion engines and more particularly, to a piston valve for a two-stroke engine.
In all two-stroke engines, a pressure ratio must be maintained across the intake and exhaust manifolds in order to force air through the cylinders. Such pressure ratio may be maintained by a low-pressure turbine, a Roots Blower, a turbocharger, etc. Other engines, for example, small two-stroke engines, pressurize the crankcase during a down stroke of the piston, and when the intake ports are uncovered, the pressurized crankcase forces air through the intake ports by way of a manifold external to the cylinder. During the compression stroke of the piston, a reed valve opens to allow additional air to enter the crankcase. The amount of air which is admitted to a cylinder of a two-stroke engine determines the amount of power that can be developed by the engine. In addition, the performance of a two-cycle engine is related to the ability of the engine to completely empty the cylinder of exhaust gases to permit the maximum amount of intake air to enter the cylinder.
Therefore, there is a need to provide an improved two-stroke engine in which the amount of air supplied to the cylinder is substantially increased.
The present invention provides an improved two-stroke engine that operates with substantially more cycle air and thus, produces more power. Further, the increased cycle air is effective to provide an improved scavenging of combustion gases from the cylinder. The increase in cycle air is provided by a simple, inexpensive and reliable valve mounted in a piston that is operated by pressure differentials within the cylinder.
According to the principles of the present invention and in accordance with the described embodiments, the present invention provides a two-stroke engine having a crankshaft, a cylinder, and a piston operatively connected to the crankshaft for reciprocating motion within the cylinder. An annular piston valve is mounted for slidable motion with respect to a centrally located inner body of the piston to control a flow of cycle air through the piston. A cycle air intake opening is located in a wall of the cylinder at a location above a bottom dead center position of the piston. The cycle air intake is blocked and unblocked by the reciprocating motion of the piston.
In one aspect of the invention, the connecting rod has a straight body section having a uniform cross-sectional area across its length, and a transition member located between the crankcase and the cylinder has a bore receiving the straight body section of the connecting rod. A seal is disposed between the bore and the straight body section of the connecting rod for blocking a flow of cycle air from the cylinder to the crankcase.
In another aspect of the invention, the annular piston valve is operated by pressure differentials within the bore of the cylinder and the piston valve has an opened position providing a fluid path between forward and rear sides of the piston, and a closed position blocking the fluid path between the forward and rear sides of the piston. The annular piston valve is forced to the closed position by a greater pressure in the cylinder on the forward side of the piston as the piston moves toward and away from the top dead center position. The cycle air intake supplies cycle air into the bore of the cylinder at the rear side of the piston as the piston moves toward and away from the top dead center position; and the cycle air intake supplies cycle air into the bore of the cylinder at the forward side of the piston as the piston moves toward and away from the bottom dead center position. The annular piston valve is forced to the opened position by a greater pressure in the cylinder on the rear side of the piston as the piston moves toward and away from the bottom dead center position to supply additional cycle air within the bore of the cylinder on the forward side of the piston, thereby providing additional cycle air for compression and combustion.
In accordance with another embodiment of the invention, a method of operating a two-stroke engine includes moving a piston in a bore of a cylinder toward, through and away from a top dead center position at one end of the cylinder. A piston valve mounted for sliding motion in the piston is maintained closed by a greater pressure on a forward side of the piston caused by motion of the piston toward the top dead center position. Cycle air is received through a cycle air intake proximate a rear side of the piston at an opposite end of the cylinder. The piston in the bore of the cylinder is moved toward a bottom dead center position at the opposite end of the cylinder, and cycle air is received into the bore of the cylinder through the cycle air intake at a forward side of the piston. Simultaneously, cycle air proximate a rear side of the piston is compressed at an opposite end of the cylinder, and the piston valve is opened in response to a greater pressure on the rear side of the piston as the piston moves toward the bottom dead center position. The piston valve is maintained open in response to the greater pressure on the rear side of the piston as the piston moves through and away from the bottom dead center position to supply additional cycle air within the bore of the cylinder on the forward side of the piston, thereby improving the scavenging of combusted air from the cylinder through the exhaust valve and providing additional cycle air for compression and combustion. The piston valve is closed in response to a greater pressure on the forward side of the piston as the piston moves toward the top dead center position.
These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein.